The present invention relates to a laser, and more particularly, to a compact waveguide gas laser of high efficiency which is effectively usable in the fields of laser material processing, coherent optical communications, and detection of enviromental pollutants, and so on.
Various waveguide lasers, each having a rectangular hollow waveguide defined by metal electrodes for producing a transverse RF discharge and dielectrics of materials such as glass or alumina, have been proposed, for instance, as disclosed by U.S. Pat. Nos. 4,169,251 and 4,352,188.
Such a transverse RF excited waveguide laser offers some advantages over a DC longitudinally excited waveguide laser in having a greater compactness, a wider tuning range, a higher efficiency (positive discharge impedance eliminates the necessity of ballast resistors), a lower excitation voltage, and longer service life due to the use of a sealed construction.
Another conventional laser, which has, instead of the composite metal-dielectric waveguide structure, all dielectric waveguide structure where the RF power is supplied to the laser gas through dielectric via external electrodes, has been known, as disclosed in an article by Christensen et al., "Transverse Electrodeless RF Discharge Excitation of High-Pressure Laser Gas Mixtures", IEEE J. Quantum Electronics, Vol. QE-16, No. 9, pages 949-954, September 1980. A waveguide laser of this type is advantageous in that it is possible to obtain a stable RF discharge and there is no ploblem associated with interaction of electrodes with the laser gas and/or sputtering of waveguide materials. However, there is a problem of relatively poor heat dissipation. In view of this problem, it is preferred to constitute the waveguide partially with metal materials such as aluminum and copper with a high thermal conductivity.
The thermal conductivities of glass, alumina, aluminum and copper are 3.2.times.10.sup.-3 cal/cm-sec.degree.C., 0.06 cal/cm-sec.degree.C., 0.487 cal/cm-sec.degree.C. and 0.923 cal/cm-sec.degree.C., respectively. The thermal conductivity of beryllia, which is a good dieletric, is as high, about 0.5 cal/cm-sec.degree.C., and hence is technically preferred as a waveguide material over materials such as glass and alumina; however, beryllia is quite toxic and therefore is generally not suitable in practice for this purpose.
In the case where metal electrodes constitute a portion of a waveguide, the narrower the width of the waveguide or the longer the length of the waveguide, the larger the waveguide loss, resulting in a lower laser output. In order to reduce the waveguide loss, it has been proposed to design the waveguide as a rectangular waveguide with enough space between opposing electrodes to eliminate the waveguiding effects of the electrodes. In such a structure, however, there may occur multi-mode oscillation in the widthwise direction of the space and/or an elliptical distribution of output beam intensity.